Equipment such as solder printers, component mounters, reflow ovens, and board inspection machines is used to produce boards mounted with many electronic components. Conventionally, this equipment is connected via board conveyance devices to form a board production line. In component mounters and board inspection machines, ball screw drive devices have been used as drive devices for mounting heads and inspection heads. In recent years, demands have risen for high speed movement and highly accurate positional control of heads, and linear motor devices have come to be used as drive devices. Of particular note are shaft type linear motor devices, which can produce a large thrust with a limited equipment space.
The present applicant has disclosed an example of this kind of shaft type linear motor device technology in patent literature 1. The cylindrical type linear motor of patent literature 1 is provided with a shaft-shaped stator assembled with a straight line of multiple permanent magnets, and a moving element with multiple in-built coils, and magnetic spacers with a limited thickness dimension are sandwiched between the permanent magnets of the stator. By this, assembly of the stator can be performed with good efficiency while curtailing any drop in thrust.
However, with a conventional linear motor, not just shaft types, when the current flowing through the coil is increased to achieve a large thrust, heat loss increases, and the temperature rises greatly. Thus, forced cooling of the coil is required using, for example, heat dissipation fins or cooling fans. Also, if strong permanent magnets are used to achieve a large thrust, the magnetic field formed by the permanent magnets influences nearby electrical components. Thus, a need arises for magnetic shielding material to mitigate the influence of the magnetic field. Examples of electrical components that require magnetic shielding (magnetic shielding target objects) are electronic control components such as CPUs, and detection sensors that detect using changes in a magnetic field. Technology for magnetic shielding in a linear motor device is disclosed in patent literature 2 and 3.
The paired linear motor of claim 4 of patent literature 2 has a configuration in which a moving element configured from 4N sets of magnet pairs and yokes is surrounded by a magnetic shield. Further, in embodiment 2 of patent literature 2, a configuration is disclosed in which two layers of magnetic shielding are provided such that a larger part of the moving element is surrounded. This is such that magnetic field leakage from the moving element is reduced.
The electric machine of claim 1 of patent literature 3 is provided with a first operating portion, a second operating portion, and a sensor device for detecting the movement amount (relative movement amount) between the two operating portions. Further, the sensor device that responds to stray fields is mounted on one of the operating portions, and a magnetic shielding device is provided between the sensor device and at least one of the operating portions. With claim 2 of patent literature 3, the electric machine is configured as a linear motor, with a first primary portion (moving body) as the first operating portion, and a secondary portion (path member) as the second operating portion. In an embodiment of patent literature 3, the sensor device is mounted on the moving body and is a position detecting sensor that scans a measurement instrument (linear scale) of the path member. Also, the magnetic shielding device is formed of a simple small shielding plate provided between the permanent magnets of the path member and the sensor device of the moving body.
Note that linear motor devices are used not only in component mounters and board inspection machines, but in various industrial machines that have a moving section which moves in a straight line.